In products comprising a number of individual ingredients it is frequently desirable to premix these ingredients sufficiently to provide a uniform slurry which is suitable either for immediate use or for further processing in other mixing apparatus. Premixing apparatus for this purpose may include a cylindrical housing with a centrally disposed rotatable shaft. A number of rotor blades are mounted on the central shaft so that they extend outwardly toward the surrounding housing and a number of cooperating stator blades are mounted about the outer wall of the cylindrical housing so that they extend inwardly toward the shaft interdigitating with the rotors. In operation the central shaft rotates causing the attached rotor blades to pass between the stator blades thereby mixing and beating a mixture of ingredients introduced into the housing causing these ingredients to form a uniform slurry.
In prior art devices of this type the individual rotor and stator blades consisted of elongated substantially bar-like members oriented at a uniform angle to the horizontal plane such that when the shaft rotated the rotors impelled the ingredients to be mixed downwardly within the cylindrical housing. In such an apparatus centrifugal force causes a vortex to form about the central shaft and the ingredients tends to ride up along the outer wall of the housing where they are incompletely mixed. If such apparatus is filled to capacity, material can spill out of the housing during operation. With such prior art premixers ingredients introduced into the top of the housing often failed to mix adequately within an acceptable period of mixing time because of the lack of circulation of the ingredients within the housing.
In commercially useable premixing apparatus of the type described above, it is important to provide thorough mixing of a maximum quantity of ingredients in a minimum time without the incorporation of air into the mixture. Air should be excluded during this premixing step so that controlled amounts of air may be introduced into the mixture in later processing steps.
With prior art apparatus the user has to choose between two equally unsatisfactory alternatives. He could achieve adequate mixing in a relatively short time if the cylindrical housing was filled to only approximately 80% of its capacity or he could fill the housing to its capacity which would require mixing times up to five times as long. Since such long mixing times were unacceptable most users chose to utilize only 80% of the rated capacity of their equipment. Because of the large vortex about the central shaft and the tendency for material to climb up along the outer housing wall, such prior art apparatus also tended to introduce varying amounts of air into the slurry.
The above deficiencies of the prior art apparatus are overcome in the present apparatus by utilizing an improved configuration for the rotor and/or stator blades of the premixer. The use of rotor and/or stator blades of the inventive configuration results in better overall circulation of the ingredients introduced into the cylindrical housing and provides more thorough mixing of a larger quantity of material within a far shorter time then prior art devices as described above while avoiding the introduction of air into the premixed slurry.